Allogeneic Interactions Research Articles

EFFECTS OF FEMALE BLOOD AUTOSERUM ON ALLOGENIC INTERACTIONS IN SHORT-TERM LYMPHOCYTE CULTURES OF PARENTS HAVING CHILDREN WITH CONOTRUNCAL HEART MALFORMATIONS

Highlights The findings of this original study ensure the detection of violations in the humoral regulation of the maternal immune interactions with semiallogeneic fetus, considered as a risk factor for developing sporadic conotruncal heart malformations in the next generation.Aim To study the role of female autoserum blood in limiting allogeneic interactions in short-term lymphocyte cultures of parents having children with conotruncal heart malformations.Methods 21 married couples (the study group) with children suffering from conotrucnal heart malformations (Tetralogy of Fallot) without chromosomal diseases were examined. The control group consisted of 21 families with three or more healthy children. The immune response in a mixed lymphocyte culture of parents was assessed by the increase in HLA-DR expression in the mixed culture with respect to spontaneous lymphocyte cultures. Primary staining of female and male lymphocytes with monoclonal antibodies to CD45, conjugated with various fluorescent dyes (PC-5 and PC-7), allowed assessing the immune response of female lymphocytes to male and vice versa.Results The effects of female autoserum on the mixed lymphocyte culture of parents were assessed. The obtained results reported that the birth of children with conotruncal heart malformations is associated with the interfering effect of female autoserum on HLA-DR expression on subpopulations of female lymphocytes (CD3+, HLA-DR+) and the activating effect on subpopulations of female lymphocytes (CD3-, HLA-DR+). The observed role of female autoserum in the study group may be associated with the absence of HLA-DR-blocking autoantibodies and high synthesis of cytokines by T2 and T3 helper lymphocytes.Conclusion The effects of female autoserum on allogeneic lymphocyte interactions of parents may be observed in short-term mixed lymphocyte cultures. The evaluation of the activating and interfering effects ensures timely identification of any violations in the humoral regulation of the maternal immune interactions with the HLA semiallogenic fetus, considered as a risk factor for developing sporadic conotruncal heart malformations in the next generation.

PECULIARITIES OF ALLOGENIC INTERACTIONS IN THE SHORT-TERM CULTURE OF LYMPHOCYTES OF SPOUSES WHO HAVE CHILDREN WITH CONGENITAL HEART DISEASES OR EARLY REPRODUCTIVE LOSSES

We have studied HLA allogeneic interactions in short-term cultures of lymphocytes from the parents having children with congenital heart defects (CHD), or subject to early reproductive losses. Twentyone married couples (CHD as the main group) who had children with sporadic CHD (interventricular septal defect) without chromosomal diseases were observed. Fifty married couples (a comparison group) had two or more reproductive losses in early gestation (up to 9 weeks), denoted as PNPs (miscarriages, missed abortions, habitual miscarriages. Forty-one families with three or more healthy children represented a control group. Immune response in cell cultures was evaluated by increasing expression of HLA-DR in a mixed culture, as compared to spontaneous lymphocyte cultures. Initial labeling of female and male lymphocytes with monoclonal antibodies to CD45 conjugated to different fluorescent dyes (PC-5 and PC-7) allowed us to evaluate the immune response of female lymphocytes to males and vice versa. The suppressor effect of autologous female serum upon the mixed culture of the lymphocytes of the spouses was also evaluated. Results of the present study showed a difference in HLA allogeneic interactions in the short-term culture of lymphocytes registered for spouses with reproductive losses and children with congenital heart defects. Reproductive losses were associated with a low blocking effect of female auto-serum upon allogeneic HLA interactions in the short-term culture of the lymphocytes of the spouses. Congenital heart defects were associated with high activity of female B-lymphocytes (CD3-/HL-DR+) in short-term mixed culture of lymphocytes from the spouses.

Extracellular Vesicles Released by Allogeneic Human Cardiac Stem/Progenitor Cells as Part of Their Therapeutic Benefit.

The positive effects of therapeutic human allogeneic cardiac stem/progenitor cells (hCPC) in terms of cardiac repair/regeneration are very likely mediated by paracrine effects. Our previous studies revealed the advantageous immune interactions of allogeneic hCPC and proposed them as part of the positive paracrine effects occurring upon their application postmyocardial infarction (MI). Currently, extracellular vesicles/exosomes (EV/Exs) released by stem/progenitor cells are also proposed as major mediators of paracrine effects of therapeutic cells. Along this line, we evaluated contribution of EV/Exs released by therapeutic hCPC to the benefit of their successful allogeneic clinical application. Through tailored allogeneic in vitro human assay models mimicking the clinical setting, we demonstrate that hCPC‐released EV/Exs were rapidly and efficiently up‐taken by chief cellular actors of cardiac repair/regeneration. This promoted MAPK/Erk1/2 activation, migration, and proliferation of human leukocyte antigens (HLA)‐mismatched hCPC, mimicking endogenous progenitor cells and cardiomyocytes, and enhanced endothelial cell migration, growth, and organization into tube‐like structures through activation of several signaling pathways. EV/Exs also acted as pro‐survival stimuli for HLA‐mismatched monocytes tuning their phenotype toward an intermediate anti‐inflammatory pro‐angiogenic phenotype. Thus, while positively impacting the intrinsic regenerative and angiogenic programs, EV/Exs released by therapeutic allogeneic hCPC can also actively contribute to shaping MI‐inflammatory environment, which could strengthen the benefits of hCPC allogeneic interactions. Collectively, our data might forecast the application of allogeneic hCPC followed by their cell‐free EV/Exs as a strategy that will not only elicit the cell‐contact mediated reparative/regenerative immune response but also have the desired long‐lasting effects through the EV/Exs. stem cells translational medicine 2019;8:911&924

Extracellular adenosine is a therapeutic target for limiting graft-versus-host disease and enhancing the graft-versus-tumor effect against hematopoietic malignancy

Allogeneic hematopoietic stem cell transplantation is performed in patients with hematologic malignancies refractory to chemotherapy. However, its efficacy is often limited by the development of graft-versus-host disease (GVHD) secondary to the allogeneic interaction of donor T cells with host dendritic cells. On the other hand, the antihost cytotoxicity of donor T cells enhances the graft-versus-tumor (GVT) effect. Extracellular adenosine generated by CD73/ecto-5'-nucleotidase from ATP via AMP plays pleiotropic roles under physiological and pathological conditions by engaging four adenosine receptors. One study recently demonstrated that ATP released from damaged cells exacerbates GVHD by activating the P2X7 receptor on host dendritic cells. In this review, we summarize our recent findings on the immunosuppressive role of extracellular adenosine in GVHD and the GVT effect. We have shown that in MHC-mismatched bone marrow transplantation, CD73 deficiency, particularly in the recipient, enhanced GVHD severity because of excessive donor T-cell expansion. Severe GVHD was enhanced by repeated administration of a CD73 inhibitor or an adenosine receptor antagonist. A competitive engraftment assay identified endogenous A2AAR signaling in donor T cells as part of a regulatory mechanism by CD73-generated adenosine. Pharmacological inhibition of CD73 enhanced the GVT effect against B-cell lymphoma and improved survival in tumor-relapsing mice after transplantation. Along with our findings, we herein introduce a novel concept that CD73-generated adenosine counteracts the ATP-evoked allogeneic immune reaction as a negative regulatory mechanism in GVHD. Pharmacological manipulation of CD73 activity could be a therapeutic strategy to limit GVHD and to preserve the GVT effect against hematopoietic malignancy.

Ex Vivo Assessment of Transplantation Tolerance Using Time Lapse Microscopy.

Background: Identifying patients in whom immunosuppression might be decreased remains challenging. Ex vivo visualization of T cell-dendritic cell (T-DC) interactions has been informative in autoimmune models suggesting that a similar approach might provide a functional measure of alloreactivity. Hypothesis and methods: CBA (H-2k) CD4+ T cells were incubated with syngeneic (CBA) or allogeneic (B6, H-2b) DCs. Individual T-DC contact times were obtained by time lapse microscopy over 40 minutes. We hypothesized that contact times would differ between autologous, allogeneic and tolerised T cell populations. Results: Allogeneic interactions ranged from short (<100s) to prolonged (>2000s, Fig 1A). To distinguish simple collisions from TCR-MHC-mediated interactions, a CD4 antibody was added at a concentration known to block allogeneic T cell responses. The antibody had little impact on short-term contacts but reduced those lasting ≥500s (Fig 1B) suggesting 500s as a threshold for defining synapse-dependent interactions. In keeping with these findings, 12.3% of allogeneic interactions were ≥500s compared with 4.2% of syngeneic ones (Fig 2).Figure: No Caption available.Figure: No Caption available.To test this system in a transplant setting, CD4+ T cells were isolated from naïve CBA mice and CBA mice tolerised to B6 alloantigens using a tolerance induction protocol. While 10.7% of naïve T cell-DC interactions exceeded 500s, T cells from tolerised mice showed a 2-fold reduction in long-term contacts (5.4%, Fig 3).Figure: No Caption available.These observations indicate that assessment of T cell-DC interaction times in vitro may be an accessible and sensitive measure of alloreactivity which could potentially be used to guide minimisation of immunosuppression.

Modulation of COUP-TF expression in a cnidarian by ectopic Wnt signalling and allorecognition.

BackgroundCOUP transcription factors are required for the regulation of gene expression underlying development, differentiation, and homeostasis. They have an evolutionarily conserved function, being a known marker for neurogenesis from cnidarians to vertebrates. A homologue of this gene was shown previously to be a neuronal and nematocyte differentiation marker in Hydra. However, COUP-TFs had not previously been studied in a colonial cnidarian.Methodology/Principal FindingsWe cloned a COUP-TF homologue from the colonial marine cnidarian Hydractinia echinata. Expression of the gene was analysed during normal development, allorecognition events and ectopic Wnt activation, using in situ hybridisation and quantitative PCR. During normal Hydractinia development, the gene was first expressed in post-gastrula stages. It was undetectable in larvae, and its mRNA was present again in putative differentiating neurons and nematocytes in post-metamorphic stages. Global activation of canonical Wnt signalling in adult animals resulted in the upregulation of COUP-TF. We also monitored a strong COUP-TF upregulation in stolons undergoing allogeneic interactions. COUP-TF mRNA was most concentrated in the tissues that contacted allogeneic, non-self tissues, and decreased in a gradient away from the contact area. Interestingly, the gene was transiently upregulated during initial contact of self stolons, but dissipated rapidly following self recognition, while in non-self contacts high expression levels were maintained.Conclusions/SignificanceWe conclude that COUP-TF is likely involved in neuronal/nematocyte differentiation in a variety of contexts. This has now been shown to include allorecognition, where COUP-TF is thought to have been co-opted to mediate allorejection by recruiting stinging cells that are the effectors of cytotoxic rejection of allogeneic tissue. Our findings that Wnt activation upregulates COUP-TF expression suggests that Wnts' role in neuronal differentiation could be mediated through COUP-TF.

Interaction of human mesenhymal stromal with immune cells

Multipotential mesenchymal stromal cells (MMSCs) are the subject of increasing scientific interest due to the key role of these cells in physiological renewal and repair. Allogeneic MMSC interaction with other components of tissue processes in the environment, in particular, with immune cells is one of the most intriguing questions of modern cell physiology. MMSCs possess pronounced immunomodulatory capabilities based on their immmunoprivilege properties and the ability to suppress an immune response. This review considers the state-of-the-art in the field of MMSC immunomodulatory effects and their mechanisms. The interaction between MMSCs and immune cells is a complex, multidirectional process governed by both direct cell-to-cell interactions and soluble factors (interferon-γ, tumor necrosis factor, prostaglandin E2, hepatocyte growth factor, interleukins, etc.). The importance of physical environmental factors, primarily oxygen tension, for the characteristics of the interaction between MMSCs and immune cells is discussed.

Mounting of erratic histoincompatible responses in hermatypic corals: a multi-year interval comparison

Studies on allorecognition in the phylum Cnidaria have disclosed complex arrays of effector mechanisms, specificity and competency to distinguish precisely between self and non-self attributes, and have revealed the existence of allogeneic maturity. Here we studied allo-responses between young Stylophora pistillata colonies by following 517 allogeneic interactions between naturally settled kin aggregates and by establishing 417 forced allogeneic and autogeneic assays made of solitarily settled spat that were cut into two similar size subclones, of which one had been challenged allogeneically. Fused assays were exposed to a second allorecognition challenge, made of three allogeneic types. Whereas about half of the kin allogeneic interactions led to tissue fusions and chimera formations, none of the 83 non-sibling pair combinations were histocompatible. In contrast to previous results we recorded rejections between siblings at the age of less than two months. More challenging, we documented cases of fusions between interacting siblings at ages older than one-year-old partners, all differing from a previous study made on the same coral population more than a decade ago. Similar erratic histoincompatible responses were recorded in other pocilloporid species. We suggest that these results reflect reduced genetic heterogeneity caused by chronic anthropogenic impacts on shallow water coral populations where planulae originating from the same mother colony or from different mother colonies that are genetically related share increasing parts of their genomes. Offspring born to related parents may also reveal an increase in genomic homozygosity, and altogether impose erratic alloimmunity.

Mesenchymal stem cells do not suppress lymphoblastic leukemic cell line proliferation.

Several studies have demonstrated the immunosuppresive effects of mesenchymal stem cells (MSCs) in allogeneic or mitogenic interactions. Cell-cell contact inhibition and secretion of suppressive soluble factors have been suggested in this regard. To investigate if adipose derived MSCs could inhibit Jurkat lymphoblastic leukemia T cell proliferation during coculture. Adherent cells with the ability of cellular growth were isolated from normal adipose tissues. Initial characterization of growing cells by flow cytometry suggested their mesenchymal stem cell characteristics. Cells were maintained in culture and used during third to fifth culture passages. Jurkat or allogeneic peripheral blood mononuclear cells (PBMCs) were labeled with carboxy fluorescein diacetate succinimidyl ester and cocultured with increasing doses of MSCs or MSC culture supernatant. Proliferation of PBMCs or Jurkat cells under these conditions was assessed by flow cytometry after 2 and 3 days of coculture, respectively. Results showed the expression of CD105, CD166 and CD44, and the absence of CD45, CD34 and CD14 on the surface of MSC like cells. Moreover, initial differentiation studies showed the potential of cell differentiation into hepatocytes. Comparison of Jurkat cell proliferation in the presence and absence of MSCs showed no significant difference, with 70% of cells displaying signs of at least one cell division. Similarly, the highest concentration of MSC culture supernatant (50% vol/vol) had no significant effect on Jurkat cell proliferation (p>0.6). The same MSC lots significantly suppressed the allogeneic PHA activated PBMCs under similar culture conditions. Using Jurkat cells as a model of leukemia T cells, our results indicated an uncertainty about the suppressive effect of MSCs and their inhibitory metabolites on tumor or leukemia cell proliferation. Additional systematic studies with MSCs of different sources are needed to fully characterize the immunological properties of MSCs before planning clinical applications.

Regulatory Allospecific NK Cell Function Is Differentially Associated with HLA C Allotypes

Major histocompatibility complex I (MHC I) molecules 'silence' natural killer (NK) cell activity. Conversely, NK cell activity is triggered through cells lacking expression of autologous MHC I. Unexpectedly we found that a subset of NK cells is activated rather than silenced when interacting with cells expressing normal levels of autologous MHC I. Instead of inducing an inflammatory phenotype, however, activation led to the secretion of the regulatory cytokines TGF-beta and IL-10. Importantly, in vitro models of allogeneic interactions showed that targets co-expressing HLA C1 and C2 epitopes best supported, or even enhanced, this cell-contact-mediated regulatory NK cell function. Together, these data ascribe a novel pattern of reactivity to NK cells, with potential implications both in autologous and allogeneic systems.

A Hypervariable Invertebrate Allodeterminant

Colonial marine invertebrates, such as sponges, corals, bryozoans, and ascidians, often live in densely populated communities where they encounter other members of their species as they grow over their substratum. Such encounters typically lead to a natural histocompatibility response in which colonies either fuse to become a single, chimeric colony or reject and aggressively compete for space. These allorecognition phenomena mediate intraspecific competition, support allotypic diversity, control the level at which selection acts, and resemble allogeneic interactions in pregnancy and transplantation. Despite the ubiquity of allorecognition in colonial phyla, however, its molecular basis has not been identified beyond what is currently known about histocompatibility in vertebrates and protochordates. We positionally cloned an allorecognition gene by using inbred strains of the cnidarian, Hydractinia symbiolongicarpus, which is a model system for the study of invertebrate allorecognition. The gene identified encodes a putative transmembrane receptor expressed in all tissues capable of allorecognition that is highly polymorphic and predicts allorecognition responses in laboratory and field-derived strains. This study reveals that a previously undescribed hypervariable molecule bearing three extracellular domains with greatest sequence similarity to the immunoglobulin superfamily is an allodeterminant in a lower metazoan.

Tricks with tetramers: how to get the most from multimeric peptide-MHC.

The development of fluorochrome-conjugated peptide-major histocompatibility complex (pMHC) multimers in conjunction with continuing advances in flow cytometry has transformed the study of antigen-specific T cells by enabling their visualization, enumeration, phenotypic characterization and isolation from ex vivo samples. Here, we bring together and discuss some of the 'tricks' that can be used to get the most out of pMHC multimers. These include: (1) simple procedures that can substantially enhance the staining intensity of cognate T cells with pMHC multimers; (2) the use of pMHC multimers to stain T cells with very-low-affinity T-cell receptor (TCR)/pMHC interactions, such as those that typically predominate in tumour-specific responses; and (3) the physical grading and clonotypic dissection of antigen-specific T cells based on the affinity of their cognate TCR using mutant pMHC multimers in conjunction with new approaches to the molecular analysis of TCR gene expression. We also examine how soluble pMHC can be used to examine T-cell activation, manipulate T-cell responses and study allogeneic and superantigen interactions with TCRs. Finally, we discuss the problems that arise with pMHC class II (pMHCII) multimers because of the low affinity of TCR/pMHCII interactions and lack of 'coreceptor help'.

Activation of Human Microvascular Endothelial Cells with TNF-Alpha and Hypoxia/Reoxygenation Enhances NK-cell Adhesion, but not NK-Cytotoxicity

Ischemia/reperfusion injury (I/R) and cellular rejection in solid organ transplantation are characterized by adhesion molecule up-regulation on the graft endothelium, a prerequisite for leukocyte recruitment. The contribution of NK cells to I/R and allograft rejection is not well understood. The aim of the present study was to investigate allogeneic interactions between human NK cells and microvascular endothelial cells (MVEC) with special regard to the differential impact of TNF-alpha and hypoxia/reoxygenation in an in vitro model of I/R. MVEC were stimulated in vitro for 8 h with TNF-alpha, exposed to hypoxia (1% O2), hypoxia/reoxygenation, and combinations thereof in a hypoxia chamber. Cell surface expression of adhesion molecules on MVEC was analyzed by flow cytometry, and adhesion molecule shedding by ELISA. NK cell adhesion on MVEC was determined under shear stress, and NK cytotoxicity using Cr-release assays. Surface expression of ICAM-1, VCAM-1, and E-/P-selectin on MVEC was up-regulated by TNF-alpha but unaffected by hypoxia/reoxygenation in the absence of TNF-alpha. ICAM-1 expression was further increased by a combination of TNF-alpha and hypoxia/reoxygenation, whereas TNF-alpha-induced E-/P-selectin expression was strongly reversed by hypoxia/reoxygenation. NK cell adhesion increased after exposing MVEC to TNF-alpha and hypoxia/reoxygenation. Susceptibility of MVEC to NK cytotoxicity was enhanced by TNF-alpha and slighty reduced by hypoxia/reoxygenation. Endothelial activation with TNF-alpha, but not hypoxia/reoxygenation, induced NK cytotoxicity whereas the combination thereof induced the strongest NK cell adhesion. Our findings suggesting a role for NK cells in allograft responses support the development of anti-inflammatory treatment strategies to prevent I/R.

Conditioning intensity and dendritic cell (DC) activation: Implications for GVHD control using DC depleting antibodies

Graft versus host disease (GVHD) is a major limitation to the widespread application of allogeneic haematopoietic stem cell transplantation (HSCT). Dendritic cells (DC) are central to allogeneic transplant interactions. Preparative myeloablative conditioning (MAC) regimens aim to ablate the host immune response and allow haematopoietic reconstitution. Conditioning also facilitates cytokine release and the host DC/donor T cell interactions that initiate GVHD. Reducing the intensity of conditioning (RIC) regimens can maintain immune anti-leukaemic activity and reduce treatment related mortality but the overall incidence of GVHD is unchanged.

Conditioning Intensity and Dendritic Cell (DC) Activation: Implications for GVHD Control Using DC Depleting Antibodies.

Graft versus Host Disease (GVHD) and treatment related mortality (TRM) are the major limitations to the widespread application of allogeneic haematopoietic stem cell transplantation (HSCT) for haematological and non-haematological malignancies. Dendritic cells (DC) as the key initiators and directors of the immune response are central to allogeneic transplant interactions. Preparative conventional conditioning (CC) regimens aim to control disease and ablate the host immune response to facilitate normal haematopoietic reconstitution. The conditioning also unleashes a cytokine storm that activates the residual host immune system, driving host DC and donor T cell interactions that result in GVHD. Reducing the intensity of conditioning (RIC) regimens maintains immune anti-leukaemic activity of T replete HSCT, reduces TRM and delays the onset of GVHD, but the overall incidence of GVHD is unchanged. We hypothesise that this is due to increased persistence of host DC. We propose that strategic administration of DC depleting antibodies could be an effective means to control GVHD. Whilst there is some information on the effects of CC on DC; we have shown that mature plasmacytoid (p) DC are increased in mouse spleen after conditioning by radiation, there is no information on the effects of RIC on DC. We have established murine models of conditioning (CC = Cyclophosphamide [CY] + 800cGy and RIC = Fludarabine [FLU] + CY + 200cGy). The effects on DC numbers, activation and subset composition (myeloid (m) DC and DC), cytokine and systemic endotoxin levels were studied on each day of the conditioning regimens in the absence of HSCT. Mice receiving CC have a significantly higher percentage of DC which are pDC compared to RIC (p<0.001) which results in a decrease in the overall percentage of mDC. However, mice that received RIC have significantly higher absolute numbers of host pDC than CC mice. Preliminary data shows no difference in endotoxin levels in mice receiving RIC or CC without HSCT. However, there may be a transient increase in endotoxin levels in mice after 2 FLU injections (p=0.12). No such increase was seen after CC. There were significantly higher levels of TNF-α (p=0.02) and IL1-β (p=0.03) in mice receiving RIC rather than CC without HSCT. The higher absolute numbers of DC, altered subset ratio and cytokine production appears to account for the delayed onset of GVHD in RIC transplant recipients. Intra-peritoneal (ip) injection of N418, a monoclonal antibody to mouse leukocyte integrin CD11c depleted murine DC in vivo. Preliminary experiments show elimination of 50% of DC after injection of N418 (500mg). Subsequent experiments show that 1mg of N418 is sufficient to significantly delay, but not prevent, GVHD in a full MHC mismatched model of HSCT (p=0.025). The action of N418 is specific, as DC depletion was not seen in mice treated with 1 mg hamster Ig. Together, these observations suggest that increasing antibody concentration and prolonged administration may be required to prevent GVHD. The successful application of DC depletion to control GVHD will improve the safety of HSCT for patients with leukaemia.

The pink-blue spot syndrome in Acropora eurystoma (Eilat, Red Sea): A possible marker of stress?

The appearance of pink-blue spots (termed here as pink-blue spot syndrome – PBSS) in the branching coral Acropora eurystoma from the Gulf of Eilat, Red Sea, is described. We monitored 18 transects (10×1 m 2 each) in front of the H. Steinitz Marine Laboratory (Eilat), at 3, 6 and 9 m depth, during March and August in 2001 and 2002. Transect measurements revealed high frequencies of colonies with PBSS (up to 100% of colonies) between 3 and 9 m depth. Ten PBSS-affected colonies of A. eurystoma were labelled and monitored for the development of spots. From March to August 2001, the number of spots per colony increased and remained constantly high at both sampling dates in 2002. Spot size ranged between 7 and 149 mm 2. Spots were primarily recorded in areas where coral tissues contacted foreign biological matter, either around regenerative wounds or when surrounded by encrusting organisms, in fast-growing areas and in allogeneic interactions. A preliminary biochemical examination suggested that the pink-blue pigment in A. eurystoma is part of a family of compounds (pocilloporin) responsible for the pink-blue colours in pocilloporid and acroporid corals. Pink-blue colour could be experimentally induced in A. eurystoma by tissue-to-tissue contacts between distressed and non-distressed allogeneic branches. PBSS was also induced in healthy coral tissue by contact with inert objects, e.g., by bandaging a branch with plastic strips. Any specific pink-blue colour spots faded within 1–3 months from onset. These results suggest that PBSS in A. eurystoma may not be considered a regular coral disease, but rather a locally induced syndrome caused by restricted environmental and/or biological stress conditions.

Allogeneic interactions in Hydractinia: is the transitory chimera beneficial?

The colonial marine hydroid, Hydractinia, exhibits four possible outcomes to allogeneic contacts: passive rejection, aggressive rejection, stable fusion and transitory fusion. In the special case of transitory fusion, Hydractinia colonies undergo tissue fusion, followed by tissue death at the original contact area, and colony separation. This type of rejection is different in several aspects from the rejection process that accompanies incompatible encounters. It has been suggested that in transitory fusion, the colonies gain immediate benefits from fusion, mainly due to size increase, without succumbing to costs associated with fusion (germ line parasitism). We report a long-term observation of repeated fusion and separation cycles in clones featuring transitory fusion that revealed a slow-down of specific growth rates following fusion, and recovery in growth rates following separation. Very rapid transfer of stained material between partners in transitory chimeras provides suggestive evidence that protection against germ line parasitism is far from being guaranteed by separation. Our data cast doubt as to whether the benefits considered for transitory fusion are sustainable and support the already made suggestion that fusion with self, rather than fusion with kin, has been the major selective force governing the evolution of allorecognition in colonial invertebrates.

Differential CD52 expression by distinct myeloid dendritic cell subsets: implications for alemtuzumab activity at the level of antigen presentation in allogeneic graft-host interactions in transplantation

Alemtuzumab (anti-CD52; Campath 1-H) depletes both host and donor T cells when used in preparative regimens for allogeneic transplantation. This promotes engraftment even after nonmyeloablative conditioning and limits graft-versus-host disease (GVHD) even after unrelated or major histocompatibility complex (MHC) disparate allografts. We asked whether anti-CD52 differentially targets antigen-presenting cells (APCs), in addition to depleting T cells. Monocyte-derived dendritic cells (moDCs) expressed abundant CD52 as expected. Langerhans cells (LCs) and dermal-interstitial DCs (DDC-IDCs), however, never expressed CD52. Immunostaining of skin and gut confirmed the absence of CD52 on these resident DC populations under both steady-state and inflammatory conditions. Although anti-CD52 functions primarily by antibody-dependent cellular cytotoxicity (ADCC) in vivo, assessment of its activity in vitro included complement-dependent lysis of CD52(+) cells. Anti-CD52 did not impair DC-T-cell adhesion, diminish DC-stimulated T-cell proliferation, or alter moDC development in vitro. We propose that anti-CD52 abrogates GVHD not only by T-cell depletion, but also by removing moDCs and their precursors. This would mitigate moDC phagocytosis and presentation of host-derived antigens to donor T cells in the inflammatory peritransplantation environment, thereby limiting GVHD. The sparing of LCs and DDC-IDCs by anti-CD52, as well as the recovery of donor-derived moDCs in a less inflammatory environment later after transplantation, may allow all these DCs to exert formative roles in graft-versus-tumor (GVT) reactions and immune reconstitution. Whether these results support a separation of deleterious from beneficial graft-host interactions at the level of antigen presentation, rather than solely at the level of T cells, will require further evaluation.

T cell activation following infection of primary follicle center lymphoma B cells with adenovirus encoding CD154.

Purified, high-titer adenovirus encoding murine CD154 (Ad-CD154) or human CD154 (Ad-hCD154) was used to infect lymph node cells isolated from patients with follicle center lymphoma. Infection of lymphoma B cells with Ad-CD154 at a multiplicity of infection (MOI) ratio of 100 or higher resulted in high-level transgene expression. Additionally, upon infection of lymphoma B cells, only Ad-CD154 resulted in surface expression of CD154, despite similar, high-level expression of either human or mouse CD154 by HeLa cells infected with Ad-hCD154 or Ad-CD154, respectively. Moreover, infection of lymphoma B cells with Ad-CD154, but not Ad-hCD154 or adenovirus encoding Eschericheria coli beta-galactosidase (Ad-LacZ), induced the neoplastic B cells to express higher levels of immune co-stimulatory molecules that are required for proficient presentation of antigen to T cells. Consistent with this, we found that Ad-CD154 infected lymphoma B cells could stimulate T cells to proliferate or produce interferon-gamma in allogeneic or autologous mixed lymphocyte interactions. We conclude that lymphoma B cells can be infected with Ad-CD154 and that this significantly enhances their recognition by allogeneic or autologous T cells. As such, Ad-CD154-transduced lymphoma B cells may have potential for the active immune therapy of patients with follicle center lymphoma.

Calcineurin antagonists inhibit interferon-gamma production by downregulation of interleukin-18 in human mixed lymphocyte reactions.

Tacrolimus (FK-506) and cyclosporin A (CsA) are calcineurin antagonists used widely as T-cell immunosuppressants; however, their relative efficacy on the production of interleukin-18 (IL-18) remains undefined. We have examined the effects of FK-506 and CsA on the cytokine generation of human peripheral blood mononuclear cells (PBMCs) in mixed lymphocyte reaction (MLR) with lipopolysaccharide (LPS). We studied the levels of interleukin-18 (IL-18), IL-12, IL-10, IL-6, IL-2 and interferon-gamma (IFN-gamma) in the supernatant in allo-MLR by ELISA assay. Supernatant levels of IFN-gamma, IL-2, IL-6, IL-10 and IL-12 were detected 12 h after MLR and markedly increased thereafter. In contrast, production of IL-18 was detected at 12 h, reached a near maximum level at 24 h and decreased at 72 h. These results suggested that IFN-gamma production depended on IL-18, IL-12 and IL-2 in the early phase of MLR and depended mainly on IL-12 and IL-2 in the late phase. Both calcineurin antagonists inhibit the generation of IL-18, which plays a large role in allogeneic cell interactions, in macrophages and they also promote an equivalent down-regulation of T helper 1 (Th1) and Th2 responses in a concentration-dependent manner. About 90% of IFN-gamma production induced by MLR was inhibited by an anti-IL-18 antibody, showing that IL-18 can trigger IFN-gamma production in MLR. These results suggest that dual signaling consisting of antigen-driven nuclear factor of activated T cells (NFAT) activation and LPS-mediated NF-kappaB activation is crucial for IL-18 production in macrophages, and that IL-18 can trigger IFN-gamma production in T-cells by MLR.